This proposed research will establish a cohort of workers exposed occupationally in the past to dimethylnitrosamine. Prospective observation of their full mortality experience, from the time of first exposure, will be conducted. Expected and observed rates of death by cause will be tabulated to ascertain if unusual mortality patterns exist, initially or over a 20-year period to the present and then subsequently. Such data will have importance in assessing the potential human carcinogenicity of dimethylnitrosamine and in assessing the potential risk of environmental exposure of N-nitroso compounds.